Porous implant material

ABSTRACT

A plurality of porous metal bodies which are bonded with each other at bonded-boundary surfaces parallel to a first direction, each of the porous metal bodies has a three-dimensional network structure formed from a continuous skeleton in which a plurality of pores are interconnected so as to have a porosity rate different from another porous metal body, the pores formed in at least the porous metal body having the higher porosity rate are formed to have flat shapes which are long along a direction parallel to the bonded-boundary surface and short along a direction orthogonal to the bonded-boundary surface, entire porosity rate of a bonded body of the porous metal bodies is 50% to 92%, a compressive strength compressing in the direction parallel to the bonded-boundary surface is 1.4 times to 5 times of a compressive strength compressing in the direction orthogonal to the bonded-boundary surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to material used for an implant implantedintravitally, and in particular, relates to implant material made ofporous metal.

Priority is claimed on Japanese Patent Application No. 2010-251432,filed Nov. 10, 2010, the content of which is incorporated herein byreference.

2. Description of the Related Art

Patent Documents 1 to 3 describes implants which are implantedintravitally.

An implant (an intervertebral spacer) described in Patent Document 1 isused by inserted and arranged between centrums from which anintervertebral disk is removed. In order to easily insert the implantand prevent the implant from falling out, the implant includes a spacerbody with an upper surface and a lower surface having unique figures.

An implant (a dental implant) described in Patent Document 2 is formedfrom: a heart material which is formed from solid-columnar titanium ortitanium alloy; and a porous layer which is arranged by the heartmaterial. The porous layer is made by sintering a plurality of sphericalgrains made of titanium or titanium alloy so that a plurality ofcontinuous holes are made between the spherical grains which are boundwith each other by sintering. The spherical grains each have a surfacelayer of gold-titanium alloy, so that the adjacent spherical grains arebound with each other by the surface layers. Accordingly, the implantdescribed in Patent Document 2 is suggested as a small dental implanthaving high bound strength with a jawbone.

An implant described in Patent Document 3 is made of porous material,and includes a first part with high porosity rate and a second part withlow porosity rate. In this case, for example, by inserting the secondpart of the implant made from absolute high-density material having atitanium-inlay-shape into a hole made at the second part of the implanthaving a shape of titanium foam in green and sintering them, the secondpart is adhered by contracting the first part. The second part with lowporosity rate is used for implanting or adhesion, so that it can beprevented to waste the grains in implanting or adhesion because of thelow porosity rate.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Examined Patent Application, SecondPublication No. 4164315

Patent Document 2: Japanese Examined Patent Application, SecondPublication No. 4061581

Patent Document 3: Japanese Translation of the PCT InternationalPublication, Publication No. 2009-504207

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Since these implants are used for a part of intravital bone, excellentconherence to bone and appropriate strength for assuming a part of bone.However, the strength tends to fail if following the cohesion to bone;on the other hand, the cohesion to bone tends to be poor if followingthe strength, so that it is difficult to satisfy both of the strengthand the cohesion.

The implants described in Patent Documents 2 and 3 are considered to bepossible to satisfy the cohesion to bone and the necessary strengthsince they have a composite construction of the solid-heart material andthe porous layer or a composite construction of the first part withhigh-porosity rate and the second part with low-porosity rate. However,if metal material is used as an implant, since metal material generallyhas higher strength than that of human bone, the implant may receivemost of load on bone, so that stress shielding (i.e., a phenomena inwhich the vicinity of inserted part of the implant to bone becomesbrittle) may arise.

Therefore, it is required for the implants to have the strengthequivalent to that of the human bone. However, the human bone has acombined structure of bio-apatite having a dimetric crystal constructionwith collagen fiber, and has a strength property preferentially orientedalong a C-axis direction. Accordingly, it is difficult for the implantto approach the human bone simply by combining the structures asdescribed in Patent Documents.

The present invention is achieved in consideration of the abovecircumstances, and has an object to provide porous implant materialhaving a strength property approximate to human bone, without arisingstress shielding, and which is possible to maintain sufficient boundstrength with human bone.

Means for Solving the Problem

Porous implant material according to the present invention has aplurality of porous metal bodies which are bonded with each other atbonded-boundary surfaces parallel to a first direction, wherein each theporous metal body has a three-dimensional network structure formed froma continuous skeleton in which a plurality of pores are interconnectedso as to have a porosity rate different from another porous metal body,the pores formed in at least the porous metal body having the higherporosity rate are formed to have flat shapes which are long along adirection parallel to the bonded-boundary surface and short along adirection orthogonal to the bonded-boundary surface, a length along thebonded-boundary surface is 1.2 times to 5 times of a length orthogonalto the bonded-boundary surface in, the pores, an entire porosity rate ofa bonded body of the porous metal bodies is 50% to 92%, a compressivestrength compressing in the direction parallel to the bonded-boundarysurface is 1.4 times to 5 times of a compressive strength compressing inthe direction orthogonal to the bonded-boundary surface.

The porous implant material can be unitarily bonded to bone byinfiltrating the bone into the interconnected pores; particularly, it iseasier for the bone to be infiltrated in the porous metal body with highporosity rate. Furthermore, since the porous metal body with lowporosity rate is bonded, the compressive strength is large in thedirection of the bonded-boundary surface. Moreover, even in the porousmetal body with low porosity rate, since the pores are formed flat alongthe bonded-boundary surface, the compressive strength is large in a flatdirection. Therefore, in the bonded body, the compressive strength alongthe bonded-boundary surface is different from the compressive strengthorthogonal to the bonded-boundary surface, so that a strength propertyis anisotropic as human bone. Accordingly, by implanting the porousimplant material into a human body with according the anisotropicstrength to a directional strength property of human bone, the stressshielding can be efficiently prevented from arising.

In this case, if a ratio of the length along the bonded-boundary surfaceand the length orthogonal to the bonded-boundary surface is lower than1.2, the strength may be insufficient; if the ratio is more than 5, thepores are too low so that infiltration of bone may be too slow and thebonding may be insufficient.

If the entire porosity rate is lower than 50%, the filtration of bone isslow, so that a bound function is insufficient. If the entire porosityrate is higher than 92%, the compressive strength is low, so thatfunction as an implant of supporting bone is insufficient.

By bonding the plurality of porous metal bodies, various block-likematerials can be easily made.

Furthermore, in a case in which the porous implant material formed asdescribed above is utilized as an implant, it is possible to add aporous metal body which is bonded at a bonded-boundary surface with adifferent direction from the direction parallel to the first directionif required.

In the porous implant material according to the present invention, whenthe first direction along the bonded-boundary surface is set to an axialdirection, it is preferable that an area-occupation rate of the porousmetal body having the lower porosity rate in a cross-sectional surfaceorthogonal to the axial direction be 0.5% to 50%.

By implanting the porous implant material with according the axialdirection thereof to an axial direction of bone, it can be utilizedalong with the strength property of bone. In this case, if thearea-occupation rate is lower than 0.5% in the porous metal body withlow porosity rate, the strength of the porous implant material tends tobe insufficient; if higher than 50%, the infiltration of bone is slow,so that it tends to take long for the implant to be ossified.

In the porous implant material according to the present invention, it ispreferable that the porous metal bodies be foam metal made by expandingand sintering after forming expandable slurry containing metal powderand expanding agent.

The foam metal can be made so as to have the three-dimensional networkstructure of the continuous skeleton and the pores, and can becontrolled in the porosity rate at a wide range by foam of the expandingagent. Therefore, the foam metal can be appropriately utilized accordingas an intended part.

Moreover, in the foam metal, an opening rate at a surface can becontrolled independently of the entire porosity rate. Therefore, byraising a metallic density at the surface (i.e., reducing the openingrate), strength along the bonded-boundary surface is improved, so thatanisotropic property can be easily added in combination with thestrength property by the flat shape of the pores.

A producing method of porous implant material according to the presentinvention has steps of: forming a bonded body by bonding a plurality ofporous metal bodies, having three-dimensional network structures formedfrom continuous skeletons in which a plurality of pores areinterconnected, at bonded-boundary surfaces along a first direction, andmaking the pores in at least the porous metal body having a higherporosity rate so as to have flat shapes by compressing the bonded bodyin a direction orthogonal to the bonded-boundary surface.

Effects of the Invention

According to the porous implant material of the present invention, sincethe porous metal bodies with low porosity rate are bonded and the flatpores are made in the porous metal bodies with high porosity rate, theporous implant material has the strength property with anisotropic nearto human bone. Therefore, by utilizing the porous implant material withaccording the anisotropic strength to the direction of bone, the stressshielding can be efficiently prevented from arising. Furthermore, it iseasy for bone to infiltrate by the interconnected pores, so that thecohesion to bone can be sufficiently maintained.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view schematically showing an embodiment ofporous implant material according to the present invention.

FIG. 2 is a schematic view showing a cross-section of porous metalbodies in the porous implant material shown in FIG. 1.

FIG. 3 is a schematic structural view showing a forming apparatus forproducing the porous metal bodies.

FIG. 4 is a plan view schematically showing another embodiment of theporous implant material.

FIG. 5 is a graph showing distributions of pore diameters in the porousimplant material of examples.

FIG. 6 is a plan view showing another embodiment of the presentinvention.

FIG. 7 is a plan view showing another embodiment of the presentinvention.

FIG. 8 is a perspective view showing another embodiment of the presentinvention.

FIG. 9 is a schematic structural view showing a substantial part ofanother forming apparatus for producing the porous metal bodies.

DETAILED DESCRIPTION OF THE INVENTION

Below, embodiments of porous implant material according to the presentinvention will be explained with reference to drawings.

Porous implant material 1 of the present embodiment is made bylaminating, a plurality of plate-like porous metal bodies 4 and 5 offoam metal having three-dimensional network structure formed from acontinuous skeleton 2 in which a plurality of pores 3 areinterconnected, at bonded-boundary surfaces F parallel to a firstdirection. In the illustrated example, the porous metal bodies 4 withlow porosity rate and the porous metal bodies 5 with high porosity rateare laminated alternately. The foam metal constructing the porous metalbodies 4 and 5 is made by expanding and sintering after formingexpandable slurry containing metal powder and expanding agent and thelike into a sheet-shape as described later. In the foam metal, the pores3 are open at a front surface, a back surface, and a side surface. Thefoam metal is made close at the vicinity of the front surface and theback surface with respect to a center part of a thickness direction.

The porous implant material 1 made by laminating the porous metal bodies4, 5 of the foam metal has an entire porosity rate of 50% to 92%. Asschematically shown in FIG. 2: pores 3A in the porous metal bodies 4with low porosity rate are formed substantially spherically; pores 3B inthe porous metal bodies 5 with high porosity rate are formed flat so asto be long along the front surface (i.e., a direction along thebonded-boundary surfaces F, that is a vertical direction in FIG. 2) andshort along a direction orthogonal to the front surface (i.e., thethickness direction, that is a horizontal direction in FIG. 2). In thiscase, each pore 3B is formed so that a length Y along the front surface(i.e., the bounded-boundary surface F) is 1.2 times to 5 times of alength X orthogonal to the front surface (i.e., the bounded-boundarysurface F). Hereinafter, the pores are denoted by the reference number 3when they are not necessary to be distinct; the substantially sphericalpores are denoted by the reference symbol 3A and the flat pores aredenoted by the reference symbol 3B when they are necessary to bedistinct.

In the porous implant material 1, the first direction along thebonded-boundary surface F is set to an axial direction C when implantinginto a living body. The porous metal bodies 4 with low porosity rate ismade so that an area-occupation rate in a cross-sectional surfaceorthogonal to the axial direction C is set in a range of 0.5% to 50% inthe entire porous metal bodies 4 with low porosity rate. For example, inFIG. 1, the axial direction C is set vertical; and an area-occupationrate in a horizontal cross-sectional surface orthogonal to the axialdirection C (i.e., the occupation rate at an upper surface in FIG. 1) isset to 0.5% to 50%.

As a bonded body of the porous metal bodies 4, 5, strength whencompressing in a direction parallel to the axial direction C (i.e., alongitudinal direction of the pores 3B) shown by the arrow by acontinuous line in FIG. 2 is 1.4 times to 5 times of a strength whencompressing in a direction parallel to a direction orthogonal to theaxial direction shown by the arrow by a dotted line.

Next, a producing method of the porous implant material 1 will beexplained.

The porous metal bodies 4, 5 forming the porous implant material 1 areproduced by for expandable slurry containing metal powder, expandingagent and the like into a sheet-shape by Doctor Blade method or thelike, dehydrating the sheet so as to make a green sheet, and expandingthe green sheet after a degreasing process and a sintering process.Furthermore, a plurality of green sheets with different mix amounts ofthe expanding agent from each other are made. These green sheets arelayered and sintered so as to make a layered body of the porous metalbodies 4, 5. Then, by pressing or rolling the layered body to compressin a layered direction, the porous implant material 1 is produced.

The expandable slurry is obtained by kneading metal powder, binder,plasticizer, surfactant, and expanding agent with water as solvent.

As metal powder, for example, powder of metal or oxide thereof which isbiologically innocuous for is used, such as pure titanium, titaniumalloy, stainless steel, cobalt chromium alloy, tantalum, niobium, or thelike. These powders can be produced by hydrogenate-dehydrogenate method,atomize method, chemical process method or the like. An average particlesize of these powders is preferably 0.5 μm to 50 μm. These powders arecontained in the slurry at 30% by mass to 80% by mass.

As the binder (i.e., a water-soluble resin binder), methyl cellulose,hydroxypropyl methylcellulose, hydroxyethyl methylcellulose,carboxymethylcellulose ammonium, ethyl cellulose, polyvinyl alcohol orthe like can be used.

The plasticizer is added in order to plasticize a compact obtain byfanning the slurry. As the plasticizer, for example, polyalcohols suchas ethylene glycol, polyethylene glycol, glycerin and the like, oils andfats such as sardine oil, rapeseed oil, olive oil and the like, etherssuch as petroleum ether and the like, and esters such as diethylphthalate, di-n-butyl phthalate, diethylhexyl phthalate, dioctylphthalate, sorbitan monooleate, sorbitan trioleate, sorbitan palmitate,sorbitan stearate and the like can be used.

As the surfactant, anion surfactants such as alkyl benzene sulfonate,α-olefin sulfonate, alkyl ester sulfate, alkyl ether sulfate, alkanesulfonate and the like, nonionic surface-active agent such aspolyethylene glycol derivatives, polyhydric alcohol derivatives and thelike, and ampholytic active agent and the like can be used.

As the expanding agent, agent which can form pores in the slurry bygenerating gas can be used. For example, volatile organic solvents suchas pentane, neopentane, hexiane, isohexane, isoheptane, benzene, octane,toluene and the like, that is, anti-soluble hydrocarbon-system organicsolvent having carbon number of 5 to 8 can be used. It is preferablythat the expanding agent be contained in the expandable slurry by 0.1 to5% by weight.

The green sheet is formed for the porous metal bodies 4, 5 using theforming apparatus 20 shown in FIG. 3 from the expandable slurry Sprepared as described above.

The forming apparatus 20 forms a sheet by Doctor Blade Method, isprovided with: a hopper 21 in which the expandable slurry S is stored; acarrier sheet 22 transferring the expandable slurry S supplied from thehoper 21; rollers 23 supporting the carrier sheet 22; a blade (a doctorblade) 24 forming the expandable slurry S on the carrier sheet 22 at aprescribed thickness; a constant-temperature high-humidity chamber 25 inwhich the expandable slurry S is expanded; and a dehydrate chamber 26 inwhich the expanded slurry is dehydrated. A lower surface of the carriersheet 22 is supported by a supporting plate 27.

Forming Process of Green Sheet

In the forming apparatus 20, at first, the expandable slurry S ischarged in the hopper 21 so as to supply the expandable slurry S on thecarrier sheet 22 from the hopper 21. The carrier sheet 22 is supportedby the rollers 23 rotating to the right in the illustration and thesupporting plate 27 so that an upper surface thereof is moved rightwardin the illustration. The expandable slurry S supplied on the carriersheet 22 is moved along with the carrier sheet 22, and formed intoplate-shape by the blade 24.

Next, the plate-shape expandable slurry S is expanded in theconstant-temperature high-humidity chamber 25 with a prescribedcondition (ex., is 30° C. to 40° C. of temperature, 75% to 95% ofhumidity) with being moved for, for example, 10 minutes to 20 minutes.Subsequently, the expanded slurry S expanded in the constant-temperaturehigh-humidity chamber 25 is dehydrated in the dehydrate chamber 26 witha prescribed condition (ex., 50° C. to 70° C. of temperature) with beingmoved for, for example, 10 minutes to 20 minutes. As a result, aspongiform green sheet G is obtained. Two types of the green sheets Gare produced so as to have different extents of foaming.

Layering and Sintering Process

The two types of green sheets G obtained as above are degreased andsintered in a state of being layered alternately so that the layeredbody of the porous metal bodies 4, 5 is formed. Specifically, the binderin the green sheets G are removed (dehydrated) under a condition invacuum, 550° C. to 650° C. of temperature for 25 minutes to 35 minutes,and then further sintered under a condition in vacuum, 700° C. to 1300°C. for 60 minutes to 120 minutes.

The layered body of the porous metal bodies 4, 5 as obtained above hasthree-dimensional network structures formed from continuous skeletons inwhich a plurality of pores 3 are interconnected. The porous metal bodies4, 5 are produced by foaming and sintering the green sheet molded on thecarrier sheet 22 so that densities at vicinities of a surface being incontact with the carrier sheet 22 and the counter surface thereof, thatis, the densities at the vicinities of a front surface and a backsurface, are closer than that of a center part along a thicknessdirection to have high metallic density. In the porous metal bodies 4,5, the pores 3 are open at the front surface and the back surface.Therefore, also in the layered body of the porous metal bodies 4, 5, thepores 3 are interconnected from the front surface to the back surface.

Compression Process

Next, the layered body of the porous metal bodies 4, 5 is compressed inthe thickness direction (i.e., layered direction) by pressing or rollingat a prescribed pressure.

By the compression process, the porous metal body 5 with higher porosityrate is compressed antecedently. Accordingly, the inner pores 3B arepressed so as to have oblong shapes long along the front surface (i.e.,along the bonded-boundary surface) and short to orthogonal to the frontsurface (i.e., along the thickness direction). If the pores 3B areoblong, as the porous metal body 5, a compressive strength is higherwhen compressed in a longitudinal direction of the oblong shape than acompressive strength when compressed orthogonal to the longitudinaldirection of the oblong shape. In addition, the porous metal body 4 withlower porosity rate is almost not pressed in the compression process, sothat the pores 3A are maintained substantially spherically; however, theporous metal body 4 may be slightly pressed.

Furthermore, the porous metal bodies 4, 5 have the high density in thevicinities of the front surface and the back surface thereof. Therefore,the layered body thereof has the higher density in the vicinities of thebonded-boundary surfaces F than at the center part between thebonded-boundary surfaces F.

In the layered body, the porous metal bodies 4 with lower porosity rateare bonded, the pores 3B in the porous metal bodies 5 with higherporosity rate are pressed so as to have oblong shaped long along thebonded-boundary surfaces F, and the density is high in the vicinities ofthe bonded-boundary surfaces F. Therefore, the strength when beingcompressed in the bonded-boundary surfaces F (i.e., in the directionshown by the arrow by the continuous line in FIG. 2) is higher than thestrength when being compressed orthogonal to the bonded-boundarysurfaces F (i.e., in the thickness direction shown by the arrow by thedotted line in FIG. 2).

Next, the layered body of the porous metal material bodies 4, 5 is cutinto a desired shape. An axial direction C is set as a first, directionalong the bonded-boundary surfaces F. The layered body is cut so that,in a cross section orthogonal to the axial direction C, an occupationarea by the porous metal bodies 4 with low porosity rate is 0.5% to 50%of a total area.

In the porous implant material 1 as produced above, owing to theporosity having the porosity rate of 50% to 92% in total, it is easy toinfiltrate for bone when the porous implant material 1 is used as animplant, so that the cohesion to the bone is excellent. Moreover, sincethe compressive strength is anisotropic; and the porous implant material1 has the strength property near to the human bone. Therefore, when theporous implant material 1 is used as a part of the bone, by implantinginto a human body with according the anisotropic strength to adirectional strength property of the human bone, the stress shieldingcan be efficiently prevented from arising. Specifically, it ispreferable that the axial direction C along the bonded-boundary surfacesF of the porous implant material 1 agree with a C-axis direction of thebone.

The human bone is structured from a sponge bone at the center partthereof and a cortical bone surrounding the sponge bone. When the porousimplant material is used as the sponge bone, the compressive strength inthe axial direction C is preferably 4 to 70 MPa; and an elastic moduleof the compression is preferably 1 to 5 GPa. When the porous implant isused as the cortical bone, the compressive strength in the axialdirection C is preferably 100 to 200 MPa, and the elastic module of thecompression is preferably 5 to 20 GPa. In each case, it is preferablethat the compressive strength in the axial direction C be directional soas to be 1.4 times to 5 times of the compressive strength of thecompressive strength in the direction orthogonal to the axial directionC.

FIG. 4 shows another embodiment. In the abovementioned embodiment, theporous metal bodies 4, 5 are formed into plate-shapes and layered. In aporous implant material 11 this embodiment, the porous metal body 4 withlower porosity rate formed into a columnar-shape is surrounded by theporous metal body 5 with higher porosity rate, so that the porousimplant material is formed into a columnar-shape. Therefore, thebonded-boundary surface F is formed as a cylindrical surface. The axialdirection C agrees with a longitudinal direction of the columnar-shape.

The porous implant material 11 is produced by: Miming two types thegreen sheet having the different porosity rate by Doctor Blade Method asdescribed above; combining the green sheet for the porous metal body 5with higher porosity rate with the green sheet for the porous metal body4 with lower porosity rate by winding; sintering in the combination soas to make a columnar-shaped sintered body; and compressing the sinteredbody in a radial direction thereof by rolling. By compressing thesintered body by rolling, the pores in the porous metal body 5 withhigher porosity rate are pressed radially so as to have oblong-shapeswhich are bent along the longitudinal direction and a circumferentialdirection of the columnar-shape.

Therefore, the porous implant material 11 has the higher compressivestrength in the longitudinal direction of the columnar-shape (i.e.,along the axial direction C) as compared with the compressive strengthin the radial direction. Therefore, the porous implant material 11 isimplanted so that the axial direction C agrees with the strengthproperty of the bone.

EXAMPLES

The green sheets were made by the expanding slurry method, and then theporous metal bodies were made from the green sheets. As material, metalpowder of titanium having an average particle size of 20 pm, polyvinylalcohol as a binder, glycerin as a binder, alkyl benzene sulfonate assurfactant, and heptane as expanding agent are kneaded with water assolvent, so that slurry was made. The slurry was formed into aplate-shape and dehydrated, so that the green sheets were made. In thiscase, by varying mixing ratio or the like of the expanding agent in theslurry, two types of the green sheets were produced so as to havedifferent porosity rate after foaming. Subsequently, the two types ofthe green sheets were layered alternately, degreased and sintered, sothat layered body of the porous metal bodies was obtained.

The layered bodies of the porous metal bodies were compressed by arolling machine, and cut so that an area-occupation rate of the porousmetal bodies with lower porosity rate were 1% or 5%. Finally, pieces ofimplant material were produced. As comparative examples, non-layeredimplant material was produced by sintering a sheet of the green sheet.

FIG. 5 is a graph showing degrees of dependence of the compressivestrengths on the porosity rates and pore-shapes. With respect todifferent ratios of lengths Y of pores parallel to a compressed surfaceby the rolling machine to lengths X orthogonal to the compressedsurface, the layered bodies having different porosity rates were madeand the strengths were measured with adding compression load parallel tothe longitudinal direction of the pores.

Prolate degree of the pores in each sample was obtained by: selectingfive to ten pores in which the shapes thereof were easy to be certifiedin a photo image by an optical microscope; calculating the prolatedegrees from lengths Y and X of the selected pores from the photo image;and averaging the prolate degrees.

The compressive strengths were measured according to JIS H 7920 (Methodfor Compressive Test of Porous Metals).

As shown in FIG. 5, in a case in which the area-occupation rate of theporous metal bodies with lower porosity rate was 5%, the prolate degreewas 3.2 (i.e., Y:X=3.2:1), and the porosity rate was 72%: thecompressive strength when compressed in the direction parallel to thefront surface was 48 MPa; and the compressive strength when compressedin the direction orthogonal to the front surface was 28 MPa. Therefore,the strength when compressed in the direction parallel to the frontsurface is about 1.7 times of that when compressed in the directionorthogonal to the front surface.

It was considered that: if the area-occupation rate was small, thecompressive strength was low and a difference between the strength alongthe front surface and the strength orthogonal to the front surface wassmall; however, by adjusting the porosity rate appropriately,appropriate implants having a wide range of the compressive strength canbe produced.

The present invention is not limited to the above-described embodimentsand various modifications may be made without departing from the scopeof the present invention.

For example, in the above embodiments, two types of the porous metalbodies having the different porosity rates, i.e., the porous metalbodies with higher porosity rate and the porous metal bodies with lowerporosity rate, are bonded. However, three or more types of porous metalbodies each having different porosity rate may be bonded.

When a plurality of porous metal bodies are bonded, variousconfigurations may be carried out as shown in FIGS. 6 to 8 besides theconfigurations in which the plate-shape porous metal bodies are layeredas the above embodiments. In these drawings, the porous metal bodieseach having the different porosity rates are denoted by the samereference symbols as in FIG. 1; that is, the porous metal bodies withlower porosity rates are denoted by the reference symbol “4”, and theporous metal bodies with higher porosity rates are denoted by thereference symbol “5”. For example, in a porous implant material 12 shownin FIG. 6, the plurality of columnar-shaped porous metal bodies 5 withlower porosity rate than in FIG. 4 are provided; in a porous implantmaterial 13 shown in FIG. 7, the porous metal bodies 4 with low porosityrate and the porous metal body 5 with high porosity rate are multiplyarranged concentrically; and in a porous implant material 14 shown inFIG. 8, the porous metal body 4 with low porosity rate is formed into across-shaped block, and the porous metal bodies 5 with high porosityrate which are formed into rectangular blocks are combined at fourcorners of the porous metal body 4. In the producing processes, theporous implant materials can be made by winding a plate-shape porousmetal body around a particular metal body, or by rounding a plate-shapeporous metal body. Prolate direction of the pores is illustrated asC-direction in FIG. 8. The prolate directions of the pores in FIGS. 6, 7are orthogonal to pages.

As a bonding method, a method in which the porous metal bodies are eachsintered, and then assembled and diffusion-bonded, can be acceptedbesides the method in which the green sheets are assembled and thensintered. When compressing, the bonded bodies having the columnarconfiguration shown in FIG. 6 and FIG. 7 can be compressed in the radialdirection by rolling the bonded bodies of the porous metal bodies as theembodiment shown in FIG. 4. Also, the compression process can be carriedout in the state of the green sheets before sintering, or aftersintering.

In each case, it is important that the bonded-boundary surfaces F areparallel to the first direction. Consequently, in combination with thedirectional strength of the compressed pores, the compressive strengthalong the direction parallel to the bonded-boundary surface F can behigher than the compressive strength along the direction orthogonal tothe bonded-boundary surface F. Moreover, when using as an implant,another porous metal body can be added that is bonded at abonded-boundary surface along the other direction than the directionparallel to the prolate direction of the pores (i.e., parallel to thefirst direction) as appropriate if the directivity of the intendedstrength can be maintained.

When forming the slurry into a sheet-shape by Doctor Blade Method, thegreen sheets can be formed in a layered state by supplying expandableslurries each having different mixing rate of the expanding agent in alayered state from a plurality of hoppers as shown in FIG. 6.

Furthermore, a method of decompression-foaming can be accepted besidesthe method of expanding and forming by Doctor Blade Method.Specifically, pores and dissolved gas are once removed from the slurry,and then the slurry is stirred while adding gas, so that expandableslurry is made into a state in which bubble nucleus of the added gas aremade and distributed therein. Subsequently, the slurry including thebubble nucleus is decompressed to a prescribed pressure and maintainedat pre-cooling temperature higher than freezing point and lower thanboiling point of the slurry at the prescribed pressure, so that thebubble nucleus are expanded and the slurry in which volume thereof isincreased by the expansion of the bubble nucleus is vacuum-freeze dried.By sintering the green body obtained as abovementioned, porous sinteredbody can be produced.

INDUSTRIAL APPLICABILITY

The implant material of the present invention can be used which isimplanted into a living body as an implant such as an intervertebralspacer, a dental implant and the like.

DESCRIPTION OF REFERENCE SYMBOLS

-   1 porous implant material-   2 skeleton-   3, 3A, 3B pore-   4 porous metal body with low porosity rate-   5 porous metal body with high porosity rate-   11 porous implant material-   12 to 14 porous implant material-   F bonded-boundary surface-   C axial direction

What is claimed is:
 1. Porous implant material comprising a plurality ofporous metal bodies which are bonded with each other at bonded-boundarysurfaces parallel to a first direction, wherein each the porous metalbody has a three-dimensional network structure formed from a continuousskeleton in which a plurality of pores are interconnected so as to havea porosity rate different from another porous metal body, the poresformed in at least the porous metal body having the higher porosity rateare formed to have flat shapes which are long along a direction parallelto the bonded-boundary surface and short along a direction orthogonal tothe bonded-boundary surface, a length along the bonded-boundary surfaceis 1.2 times to 5 times of a length orthogonal to the bonded-boundarysurface in the pores, an entire porosity rate of a bonded body of theporous metal bodies is 50% to 92%, and a compressive strengthcompressing in the direction parallel to the bonded-boundary surface is1.4 times to 5 times of a compressive strength compressing in thedirection orthogonal to the bonded-boundary direction.
 2. The porousimplant material according to claim 1, wherein when the first directionalong the bonded-boundary surface is set to an axial direction, anarea-occupation rate of the porous metal body having the lower porosityrate in a cross-sectional surface orthogonal to the axial direction is0.5% to 50%.
 3. The porous implant material according to claim 1,wherein the porous metal bodies are foam metal made by expanding andsintering after forming expandable slurry containing metal powder andexpanding agent.
 4. The porous implant material according to claim 2,wherein the porous metal bodies are foam metal made by expanding andsintering after forming expandable slurry containing metal powder andexpanding agent.
 5. A producing method of porous implant materialcomprising steps of: forming a bonded body by bonding a plurality ofporous metal bodies, having three-dimensional network structures formedfrom continuous skeletons in which a plurality of pores areinterconnected, at bonded-boundary surfaces along a first direction, andmaking the pores in at least the porous metal body having a higherporosity rate so as to have flat shapes by compressing the bonded bodyalong a direction orthogonal to the bonded-boundary surface.